Quarterly report pursuant to Section 13 or 15(d)

Stock-Based Compensation Narrative (Details)

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Stock-Based Compensation Narrative (Details) - 2007 Stock Incentive Plan - shares
3 Months Ended 6 Months Ended
May 10, 2018
Jun. 30, 2018
Mar. 31, 2018
Jun. 30, 2017
Mar. 31, 2017
Jun. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Additional shares authorized (in shares) 500,000          
Shares authorized (in shares) 3,230,320          
Performance stock units            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Equity instruments other than options, granted (in shares)   0   0 166,149 0
Equity instruments other than options, vested (in shares)         116,168  
Shares issued (in shares)     25,726      
Award vesting rights, percentage     22.10%